This invention relates to ac plasma displays, and in particular to a display suitable for color graphics.
As known in the art, plasma display panels basically comprise a substrate and cover, both including dielectric layers over their major surfaces, which are placed so as to define a gap therebetween. A gas which is capable of being ionized, such as neon with 0.1 percent argon added, is sealed within the gap. The display is defined by locally induced glow discharges in the gas produced by applying a desired potential to selected electrodes in arrays embedded within the dielectric layers. Once a display site or "pel" is fired as a result of applying the appropriate potential during a "write" stage, it will remain "on" as an ac potential is applied to electrodes included within the site during a "sustain" stage due to the generation of charges on the surface of the dielectric layer. Typically, additional layers of a low work function material are provided over the dielectric layers to provide good electron emission, and thereby reduce the level of the required potential. It is also known that providing an appropriate phosphor layer over the cover electrodes can produce displays of various colors.
Recently, a display has been proposed where each pel includes the crosspoint region of three electrodes--a pair of metal electrodes formed on the substrate (Y electrodes), and an electrode running perpendicular thereto formed over the cover or over a dielectric on the substrate electrodes (X electrode). When the X electrode is placed on the cover, it preferably can be a transparent conductor material such as indium tin oxide or indium oxide. A display site is written, for example, by applying a negative pulse to a Y electrode and a positive pulse to the X electrode of the desired crosspoint region. This cause a glow discharge at that region and also results in the accumulation of negative charges on the dielectric over the X electrode and positive charges on the dielectric over the Y electrode. A positive pulse is then applied to the other Y electrode of the crosspoint region to transfer the negative charge to the dielectric layer thereover. The discharge is then sustained in the area over the Y electrode pair by applying an ac signal which causes successive glow discharges and shifts the charges back and forth over the two electrodes. The region remains "on" until erased by appropriate pulses applied to the electrodes which are of a shorter duration and less magnitude than the write pulses. (For a detailed discussion of such a display, see U.S. Pat. No. 4,554,537 issued to G. W. Dick and assigned to AT&T Bell Laboratories, which is incorporated by reference herein.)
In order to construct a color display from such a structure, it is desirable to provide phosphor layers over the cover electrodes. A typical structure would include adjacent areas of red, green and blue phosphor layers aligned with the electrode arrays so that each color pel would comprise a combination of three adjacent crosspoint regions of the type described above, each aligned with a different color phosphor. (See, e.g., M. Yokozawa et al., "Color TV Display With AC-PDP", Proc. 3rd Int. Research Conf., Kobe, Japan, 1983, pp. 514-517). Thus, appropriate colors could be generated by operating the right combination of crosspoint regions in the manner previously described.
The use of a phosphor layer, however, can produce some difficulties. In particular, the usual electron emission layers provided over the cover electrodes tend to attenuate the ultraviolet light produced from the glow discharge to the extent that such light may not reach the phosphor at a sufficient intensity level. It is, therefore, desirable to either remove or reduce the thickness of the electron emission layer. However, in so doing, the voltage requirements on the electrodes are increased, and this increase can cause undesired charge storage on the cover and/or charge transfer to adjacent crosspoint regions which are not meant to be ignited. This can be particularly troublesome in view of the high line density usually required for color displays.
It is, therefore, a primary object of the invention to provide a plasma display which does not require a standard secondary emitter layer and yet results in insignificant crosstalk.